The present invention relates in general to a power and communication (control) transmission system for use with an enclosed fluid apparatus such as a mud filled drill string of an oil well or other fluid filled pipe arrangement. One purpose of the present invention is to eliminate the need for a continuous electrical conductor requiring connections at each drill pipe coupling. Although the primary use of the system of this invention is for powering and/or communicating with downhole oil well drilling tools or instruments associated with the drill string, the system may also be used in association with any other type of enclosed fluid system. Most of the detailed description will, however, be directed to the use of the system in the drilling for oil.
Although there are presently available different schemes for signal communication in an oil well, there is still a need for an efficient and trouble-free system for powering and communicating with downhole tool or data gathering instruments. One communication technique employs direct cable connection between the top and bottom of the drill string. See for example, U.S. Pat. Nos. 3,918,537 and 3,879,097. This type of technique requires connection at each drill pipe section. If, for example, there is a fifteen thousand foot drill string, there are approximately five hundred joints or connections in such a length of drill pipe and there would have to also be five hundred coaxial connections. As each joint of drill pipe is connected, each connector of the cable also has to be connected. This technique drastically increases the time to lay down a string of drill pipe and also drastically increases the possibility of bad cable connections especially in long drill strings and in an environment that is quite dirty.
One improvement over such cable communication systems is a system of the type shown in U.S. Pat. No. 2,379,800 employing magnetically coupled circuits. However, again, in a long length of drill pipe there is a substantial chance for signal attenuation with such a system and in may practical applications this system is not useable.
In addition, there are systems that presently employ mud pulse telemetry. See for example U.S. Pat. Nos. 3,949,354; 3,964,556; and 3,958,217. In the Spinnler patent '217 it employs mud pulse telemetry but has disadvantages such as the fact that they restrict the flow of mud in the drill string thereby interfering with the necessary mud flow through the drill string which is used in facilitating the drilling operation; most important, they restrict the use of thru-drillpipe oil well logging tools. In the Gearhart patent '556 they are required to cease mud flow in order to provide signal communication thus definitely inhibiting the overall operation of their system. In the Claycomb patent '354 they provide for only data transmission and apparently require one or more power sources at the bottom of the well. On the other hand in accordance with the present invention there is provided relatively simple means for signal communication and also means for the transfer of power energy at one or more locations in the drill string.
Accordingly, one object of the present invention is to provide an improved telemetry and power transmission system for an enclosed fluid apparatus.
Another object of the present invention is to provide a power and communication transmission system employing control or signal wiring magnetically coupled from drill pipe section to drill pipe section.
Another object is to provide high-speed bi-directional communication.
A further object of the present invention is to provide a system in accordance with this invention that employs acoustics for power propagation in combination with electromagnetics for information propagation. The transmission of energy is by low frequency acoustics or sound waves. The acoustical pulses propagate through the fluid in the drill pipe and preferably comprise a plane acoustic pressure wave adapted to propagate in one direction down the drill string.
Still another object of the present invention is to provide a system in accordance with this invention that provides, at one or more locations, signal reinforcement means for reinforcing the control signals. The signal reinforcement means comprises an acoustic converter for detecting an acoustic power pulse and converting this acoustic signal to preferably a DC voltage signal for powering a repeater circuit or the like.
Still another object of the present invention is to provide a system in accordance with this invention employing means for establishing a plane acoustic pressure wave in the drill pipe, which pressure wave is received at the bottom of the drill pipe and converted into preferably a DC power signal for powering the tools or instrumentation at the bottom of the well.
Another object of the present invention is to provide a system in accordance with this invention wherein the acoustic generator means and the acoustic converter means are substantially non-intrusive to the normal flow of mud in the drill pipe. In accordance with the system of this invention there is preferably no substantial restriction to the mud flow during the acoustical operation, and further there is no requirement in accordance with this invention for interrupting or enhancing mud flow in order for the acoustic power transmission and the electromagnetic telemetry to take place. The only restriction is that there is mud present. In accordance with the invention the acoustic energy converter, like the acoustic power generator, permits the constant flow of mud, and yet absorbs energy from the acoustic pressure wave and converts this energy into a useable electrical energy for the telemetry system.